The magnetic field sensors with Laplace force can be used to measure a component of the Earth's magnetic field or a component of a magnetic field generated by an electrical conductor or another magnetic field source.
The expression “component of the magnetic field” designates the amplitude of the orthogonal projection of the magnetic field on a measurement axis of the sensor.
Known sensors comprise:
a substrate extending essentially in a plane called substrate plane,
at least one electrical conductor suitable for an electrical current to flow through, this electrical conductor comprising a moving part, suspended over the substrate, suitable for being displaced in a direction of displacement when it is subjected to a Laplace force,
mechanical links mechanically connecting this moving part to the substrate and electrically connecting the moving part to current power supply contact blocks arranged on the substrate,
at least one gauge suitable for measuring a physical quantity representative of the amplitude of the displacement of the moving part, this gauge comprising at least one first and one second parts,
a suspended lever that can be rotationally displaced about an axis of rotation at right angles to the direction of displacement of the moving part, this lever comprising a first and a second attachment points, the first attachment point being mechanically connected to the moving part to drive the lever in rotation about the axis of rotation in response to a displacement of the moving part, and the second attachment point being directly mechanically connected to the first part of the gauge.
For example, such sensors are described in the following papers A1 and A2:    A1: V. Beroulle et al., “Monolithic piezoresistive CMOS magnetic field sensors”, Sensors and actuators A, vol 103, pages 23-32, 2003,    A2: A. L. Herrera-May et al., “A resonant magnetic field microsensor with high quality factor at atmospheric pressure”, J. Micromechanical Microengineering, 19 (2009) 015016.
Prior art is also known from:
U.S. Pat. No. 7,642,692 B1, and
US 2006/076947.
It is desirable to optimize these sensors, notably to enhance their sensitivity or set their bandwidth. However, in practice, this task proves particularly difficult to carry out. This point is illustrated by the following few examples.
To increase the sensitivity of the sensor described in the paper A1 or A2, moving the electrical conductor on which the Laplace force is exerted away from the gauge by increasing the length of the lever could be envisaged. In effect, increasing the length of the lever makes it possible to increase the force which is exerted on the gauge, and therefore increase the sensitivity of the sensor. However, increasing the length of the lever alters the resonance frequency of the lever. Now, the electrical conductors of the sensors of the papers A1 and A2 have to be powered with an alternating current whose frequency is chosen to be equal to the mechanical resonance frequency of the lever. Consequently, increasing the length of the lever results in working at frequencies which can be located outside the desired working frequency range. For example, the lower the working frequency, the more sensitive the sensor is to mechanical vibrations. Furthermore, in the case of the papers A1 and A2, the gauges are integrated on the lever. In these conditions, for the gauges to be able to measure a strain variation, the lever has to be deformable. In effect, if it is not deformable, the gauges do not measure any signals. Consequently, since the lever is deformable, there is no mechanical lever arm effect to be directly profited from by increasing the length of the lever. To obtain this effect, the lever would have to be rigid.
In the known sensors, if a given bandwidth is desired for the sensor, it is also necessary to adjust the length of the lever and/or the stiffness of the mechanical links. In the same way as what has been stated above, these modifications also necessarily alter the sensitivity of the sensor, which is not desired.
Finally, in the known sensors, it is also possible to envisage reducing the stiffness of the mechanical links to increase the amplitude of the displacement of the moving part of the electrical conductor. However, yet again, such a modification cannot be made without altering other aspects of the operation of the sensor such as its resonance frequency.